Display technology in recent years has undergone fast development; flat-panel displays are significantly distinguished from traditional displays for completely different display mode and manufacturing technologies. Flat-panel displays have features of being flat, light, thin and power-saving and are in compliance with the inexorable development trend of image displays in the future. So far, flat panel displays mainly include: thin-film transistor liquid crystal displays (TFT-LCDs), plasma display panels (PDP), and organic light-emitting diode displays, etc.
A thin-film transistor liquid crystal display (TFT-LCD) has features of small size, low power consumption and no radiation, etc, which has been developed rapidly in recent years and occupies a leading position in the current flat-panel display market. At present, TFT-LCDs have been applied widely in various products of large, medium and small sizes, covering almost all the popular electronic products in the present information society, such as high-definition digital TVs, (desktop and laptop) computers, mobile phones, PDAs, GPS, on-board displays, projectors, camcorders, digital cameras, electronic watches, calculators, electronic instruments, instrumentation, public displays, and virtual displays, etc., and surpass any other type of flat-panel display.
For a TFT-LCD, a TFT array substrate and a manufacturing process thereof determine its performance, yield, and product price. Because a masking process for patterning is complex and of high-cost, the number of masks (i.e., patterning times) to be used in a preparation process of a TFT array substrate has becomes an important factor to measure the complexity of the manufacturing process. Therefore, reducing the number of masks and exposure times in a manufacturing process of a TFT array substrate has become a key issue to improve the manufacturing process.
There are many methods to reduce the number of masks to be used in a preparation process. At present, the most commonly used are a Gray-Tone Mask (GTM) and a Half-Tone Mask (HTM). By utilizing these techniques, the number of masks and exposure times so far commonly used in a preparation process of a TFT array substrate, is four, that is, three ordinary masks plus one GTM or HTM. Although the number of masks and exposure times has been reduced to four, there are still disadvantages, for example inefficient productivity and equipment utilization, etc.